SIM cards have become established as a standard for authentication of a user of a GSM mobile radio. In conventional GSM appliances, such as a mobile telephone, the card reader for SIM cards is integrated in the appliance. Further, as the functionality of GSM appliances increases, the importance of the SIM card is also growing since it is no longer used solely for checking the authorization to make telephone calls but for different applications, such as access authorization to secure areas, that is to say in the end as a key substitute, or for payment functions.
During this process, it has been found that, for some applications, it is desirable for the SIM card reader to be physically separated from the GSM appliance. For example, the SIM card may be inserted in an appropriate card reader in a motor vehicle in order in this way to authenticate a user for a GSM system in the vehicle. Furthermore, both in the private field and in the commercial field, a user may be authenticated via a SIM card reader for telephone systems, computers, network parts, automatic payment devices, or other appliances with GSM functionality. In this case, for security reasons, the aim is to provide a direct link between the card reader and the GSM appliance for the transmission of the authentication data and, in applications mentioned, this direct link often has to have a length of several meters, owing to the physical characteristics.
Generally, however, the electrical drivers for the SIM card interface in GSM modems are designed only for distances of less than 50 cm.
Integrated circuits are admittedly available which allow an “extension” to several meters. However, since the data line to the SIM card is designed to be bidirectional, these circuits require a control signal for the signal direction. However, no such signal is externally available on standard GSM modems. Circuits such as these are therefore designed only for direct integration in GSM modems and, furthermore, they are costly.
Another possibility is to use GSM modems with a remote access function for SIM data (so-called Remote SIM Access—RSA). In this case, the data is read in and out from the SIM card at a remote point, and is interchanged between the GSM modem and the SIM card by means of AT commands (Hayes standard command set for modems, of ATtention). The data may in this case be transmitted by wire or radio (for example Bluetooth). However, this solution is costly and, furthermore, depends on the use of GSM modems with RSA functionality, which are commercially available only in small numbers.